Washington: The passenger name records of the airlines travel, commonly known as PNR, has emerged as one of the key tolls in many prominent terror investigations including the Mumbai terrorist attack and Times Square bomb plot, US lawmakers and experts have said.

"PNR has played a key role in many prominent terror investigations, including that of the 2008 Mumbai attack plotter David Headley and the attempted Times Square bomber, Faisal Shahzad," said Congressman Jackie Speier at a Congressional hearing.

Congressman Patrick Meehan, who chaired the Congressional hearing on "Intelligence Sharing and Terrorist Travel: How DHS Addresses the Mission of Providing Security, Facilitating Commerce and Protecting Privacy for Passengers Engaged in International Travel," said in 2008 and 2009, PNR helped theUS identify individuals with potential ties to terrorism in more than 3,000 cases.

"Among these was the Mumbai attack plotter David Headley, who was arrested in Chicago after US authorities accessed his PNR data from a flight he had booked from the United States to Germany. Headley has since pled guilty to a separate plot to murder journalists from a Danish newspaper," he said.

"PNR data also identified Faisal Shahzad, the perpetrator of the failed Times Square bombing in May 2010, who was caught with the help of PNR as he attempted to escape the United States at JFK Airport. In 2010, approximately one quarter of those individuals denied entry into the United States for having ties to terrorism were initially tied through PNR data," Meehan said.

PNR, Speier said, can be immensely important to terrorism investigations.

"Investigators can use a terror suspect's past travel history to identify travel to terror safe havens, as well as co- travelers who may be associates, which can help to identify and disrupt the entire terror network," he said.

PNR is the data that an airline receives from travelers to book and manage their reservations. This can include the traveler's itinerary, payment method and contact information, said Thomas Bush of the Customs and Border Protection.

"It is one of our most important tools in the ongoing fight against terrorism, as well as narcotics smuggling, human trafficking and other transnational crime," he said.

"One important example of it is the case of Najibullah Zazi-- the al-Qaeda trained operative who planned to explode improvised explosive devices in the New York City subway system," he said.

"Using PNR data, DHS and CBP worked closely with the FBI to crosswalk the names of his co-travelers against open counter-terrorism cases inside the United States and determined his co-travelers were being trained during the same trips to Pakistan in the same training camps. Zazi was arrested on September 19th, 2009, and the information from his PNR records were used in his questioning and his indictment. Zazi pled guilty in February 2010," Bush said.

"Another example of CBP's ability to fully leverage PNR's holdings is specifically about those who we have very little information or those we call the unknowns. Law enforcement intelligence information implicated a specific person in the plotting of a 2008 Mumbai attack, as well as the possible attacks against a Danish newspaper office," he said.

"Starting with a very common first name, David, a partial travel itinerary and a very vague travel timeframe, CBP was able to review its PNR data in connection with other DHS databases," Bush said.

"Within 24 hours, CBP was able to provide the FBI with the person's full name, address, passport number, travel history and other information useful to law enforcement pursuing him. You may know that person as David Headley, who pled guilty in March 2010," he said, adding that a third example of how CBP's use of PNR has been successful also demonstrates when they receive the data.

"In the case of Faisal Shahzad, who attempted to use the car bomb in Times Square in May 2010, CBP used PNR in the first place to target him on his flight returning from Pakistan. It was also used to intercept him when he tried to flee the plot after it was unsuccessful.

"After a stay in Pakistan, in which it was later, determined Shahzad underwent terrorist training, he arrived in the US and was flagged for screening based on information in his PNR. CBP conducted an examination and released him after finding no reason to further detain him," he said.

PNR, Bush said, uniquely and solely provides CBP with the ability to identify the true point of origin for travel.

"Without it, CBP often mistakes the origin of travel as that last point of departure to the United States. Take an example for Heathrow versus an originating travel in Pakistan.

PNR also allows CBP to see all the stops along the way. PNR also affords CBP the opportunity to determine suspicious booking and payment methods, such as last-minute ticket purchase, cash tickets or one-way tickets," he added.